Oxygen, helium, and other gases commonly are supplied to the user in relatively heavy cylindrical tank-like containers of various sizes. The tanks typically are transported to the user in a truck trailer, and empty tanks are similarly returned to the supplier for refill. Such free standing gas containers can easily topple during handling and transport, which can not only damage the containers and surroundings, but also create a risk of explosion. To retain the cylindrical containers in upright condition during transport, it has been proposed to secure the containers to the walls of the truck trailer, such as by means of retaining straps or brackets. Since the containers when filled each may weigh as much as 150 pounds and the truck trailer walls usually are not reinforced, forces acting on the heavy containers during transport can cause the straps or retaining brackets to be torn out of the wall. As a result, it has not been possible to transport large numbers of such containers at the same time. Present container retention devices furthermore do not facilitate retention of large numbers of empty containers for return to the supplier for refilling. Prior retention devices also often have been complicated and have impeded handling of the containers during mounting in and removal from the retention device.